The 2bn-euro venture will build a full picture of the state of the planet from satellite and ground-based data.

But despite the UK's oft-stated claim to lead the world on climate policy, it has so far been lukewarm on GMES.

Three leading scientists have now sent a letter to the PM urging him to back GMES at a critical meeting next week.

Member states of the European Space Agency (Esa) will decide at a gathering in The Hague how to fund the next phase of the Global Monitoring for Environment and Security (GMES) programme, also known as Kopernikus.

Britain will have to put up well in excess of 100m euros if it wants to have a major influence on the project. At previous opportunities, Britain has declined to play a major role and the researchers fear the outcome of the Dutch meeting will be the same.

"We strongly believe that a major UK contribution to Kopernikus is necessary to support the UK's wish to be a world leader in responding to climate change and its consequences," the scientists write.

"However, it is our current understanding that the UK may not contribute at a level concomitant with its position as one of the world's leading economies."

The signatories include Professor Alan O'Neill, the director of the UK's National Centre for Earth Observation.

"I believe this is a very important programme for the UK to take leadership in," he told BBC News.

"The programme can and will evolve into something which will be of major benefit to mankind; I don't think it is too melodramatic to say that. We need a planetary Earth-observing system to gather all the information to take remedial action on climate and environmental change."

Space jobs

The lead agency in the UK on GMES is the Department for Environment, Food and Rural Affairs. Over the past few weeks, it has consistently held the line that the UK is committed to supporting the project.

And the PM himself reinforced this position during Prime Minister's Questions in the House last month when he said: "We recognise the importance of understanding and monitoring climate change. No decision has yet been taken on the level of UK funding, but a final decision will be taken in advance of the ministerial meeting in late November."

The project calls for new satellites called Sentinels to fill data gaps

Professor O'Neill and his co-signatories, Profs Paul Monks and Shaun Quegan, are concerned that a small contribution from the UK will leave it isolated and incapable of influencing the development of GMES.

They are worried that world-leading British expertise on Earth observation instruments will be excluded as a result, diminishing the project's effectiveness; and they fear for British space jobs because satellite construction work will almost certainly be lost to other Esa member states.

"If we are a downstream recipient of data, a third-party user, we will not be involved in influencing the agenda and the prioritisation for the instruments. Our industry will not be competing to build those instruments," Professor O'Neill explained.

"And by not having close proximity to the actual data, we will lose first-mover advantage, not just in science but in downstream applications. So we're either in the vanguard and mixing it, or gradually over time we will become third division."

'Piecemeal' process

In their letter, the scientists also criticise the way space policy and decisions on space funding are made in the UK which, unlike its major European partners, does not have a dedicated Space Agency.

The scientists write: "The UK does not appear to have pursued a high-level approach to decision making about investment in Kopernikus.

"Instead, the process has been bottom-up and piecemeal, so that opportunities afforded by Kopernikus are considered within the individual brief of agencies under financial pressure."

The UK science minister Lord Drayson will deliver Britain's position on GMES to European partners when he meets his Esa counterparts in the Dutch capital on Tuesday and Wednesday.

The meeting will determine priority and funding for Esa programmes over the next three years. The agenda ranges across issues such as Europe's participation in the space station and the technology investment needed to keep Europe competitive in launch and satellite systems.

Although the second biggest economy in the agency's membership, the UK pays in less than Italy, and significantly less than France and Germany. And on optional projects, which include the astronaut and space station programmes, the UK contributes less than Belgium.

Lord Drayson did state recently, however, that he hoped Britain would one day fund an astronaut.

On the subject of the scientists' GMES letter, Adam Afriyie MP, shadow minister for science & innovation, commented: "It is disconcerting that the science minister can make unfunded promises about a British astronaut programme, yet is unable to guarantee a commitment to an existing satellite project.

"Environmental monitoring must be a national priority if the Prime Minister is serious about climate change."

Professor Monks is affiliated to Leicester University; Professor Quegan works out of Sheffield University.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.